IIHS research bibliography

IIHS has been conducting research for more than 50 years. Papers published in copyrighted publications such as books, journals and conference proceedings are available upon request, but their contents may not be redistributed or republished without consent of the publishers. Unpublished and noncopyrighted reports are available for download, and their contents may be redistributed and republished with attribution.

Objective: This study investigated the relationship between the peak sternal deflection measurements recorded by the Hybrid III 50th percentile male anthropometric test device (ATD) in frontal crash tests and injury and fatality outcomes for drivers in field crashes.

Methods: ATD sternal deflection data were obtained from the Insurance Institute for Highway Safety's 64 km/h, 40 percent overlap crashworthiness evaluation tests for vehicles with seat belt crash tensioners, load limiters, and good-rated structure. The National Automotive Sampling System Crashworthiness Data System (NASS-CDS) was queried for frontal crashes of these vehicles in which the driver was restrained by a seat belt and air bag. Injury probability curves were calculated by frontal crash type using the injuries coded in NASS-CDS and peak ATD sternal deflection data. Fatality Analysis Reporting System (FARS) front-to-front crashes with exactly one driver death were also studied to determine whether the difference in measured sternal deflections for the 2 vehicles was related to the odds of fatality.

Results: For center impacts, moderate overlaps, and large overlaps in NASS-CDS, the probability of the driver sustaining an Abbreviated Injury Scale (AIS) score = 3 thoracic injury, or any nonextremity AIS = 3 injury, increased with increasing ATD sternal deflection measured in crash tests. For small overlaps, however, these probabilities decreased with increasing deflection. For FARS crashes, the fatally injured driver more often was in the vehicle with the lower measured deflection in crash tests (55 vs. 45%). After controlling for other factors, a 5-mm difference in measured sternal deflections between the 2 vehicles was associated with a fatality odds ratio of 0.762 for the driver in the vehicle with the greater deflection (95% confidence interval = 0.373, 1.449).

Conclusions: Restraint systems that reduce peak Hybrid III sternal deflection in a moderate overlap crash test are beneficial in real-world crashes with similar or greater overlap but likely have a disbenefit in crashes with small overlap. This may occur because belt-force limiters employed to control deflections allow excursion that could produce contact with interior vehicle components in small overlaps, given the more oblique occupant motion and potential inboard movement of the air bag. Although based on a limited number of cases, this interpretation is supported by differences in skeletal fracture locations among drivers in crashes with different overlaps. Current restraint systems could be improved by designs that reduce sternal deflection in moderate and large overlap crashes without increasing occupant excursion in small overlap crashes.

Aylor, David A.; Zuby, David S.Proceedings of the 22nd International Technical Conference on the. Enhanced Safety of Vehicles (CD ROM)
2011

Abstract

The Insurance Institute for Highway Safety rates vehicle
seat/head restraint designs as good, acceptable,
marginal, or poor using a protocol by the Research
Council for Automobile Repairs’ International Insurance
Whiplash Prevention Group (RCAR/ IIWPG).
Studies of insurance neck injury claim rates for rear
impact crashes show that vehicles with seats rated
good have lower claim rates than vehicles with seats
rated poor, but the relationship between acceptable/
marginal ratings and claim rates is less clear.
To better understand the relationship between measured
neck injury criteria and injury claim rates, a series of
rear impact crash tests was conducted to determine the
influence of crash pulse, as dictated by vehicle structure,
on the performance of seat/head restraints. The
role of head restraint adjustment also was examined by
comparing BioRID responses in the driver position,
with the restraint adjusted according to the RCAR/
IIWPG protocol, and in the front passenger position,
with the restraint adjusted to its lowest position. In an
attempt to match the severity of the RCAR/IIWPG
crash pulse, vehicles were struck by a flat rigid barrier
to create a velocity change of 16 km/h (10 mi/h).
Four small cars with rated seat/head restraints and
varying real-world neck injury claim rates were selected.
The 2006 Honda Civic and 2005 Chevrolet
Cobalt both received good ratings in the RCAR/
IIWPG sled test, but the Civic had a relatively low
neck injury claim rate compared with the Cobalt. The
2006 Saturn Ion and 2005 Ford Focus both received
marginal ratings in the sled test, but the neck injury
claim rate for the Ion was comparable with that for the
good-rated Civic, and the Focus had the highest neck
injury claim rate among the vehicles tested.
BioRID response ratings for the driver position
matched the sled test ratings for the Cobalt and Focus
but were one rating level lower for the Civic and Ion.
BioRID response ratings for the passenger position
were the same as those for the driver position for all
vehicles except the Cobalt, which was one rating level
lower. The findings suggest that changing the RCAR/
IIWPG protocol to include vehicle specific crash
pulses and/or changing the restraint setup would not
improve the relationship between seat/head restraint
ratings and neck injury claim rates. Furthermore,
examination of additional BioRID injury metrics not
currently assessed under the protocol does not help
explain real-world neck injury claim rates and does
not support changing the current evaluation criteria.
Additional research is needed to determine whether
vehicle underride/override alters vehicle accelerations
in a way that makes crash tests more predictive of
neck injury claim risk in rear-end collisions.

GLORIA: Design and development of a calibration jig for H-point machines used for the measurement of head restraint geometry

The SAE J826 H-point machine was designed to measure occupant accommodation dimensions relative to a loaded seat. It has become an intrinsic part of various crash dummy set up processes, but it has never had a formal calibration procedure. Whilst H-point location appears to be consistent from one device to another, the weight hanger locations show greater variability, and this can consequently affect the height and backset measurements of head restraints taken with a head restraint measuring device mounted upon the weight hangers. This paper describes the development of a calibration procedure and jig to measure the location of the weight hangers so that adjustments can be made if necessary. This procedure and calibration tool will enable more consistent seat evaluations, dummy set up, and consistently effective anti-whiplash seat designs.

A new calibration specification for linear displacement transducers

Linear displacement transducers may be used to measure deflection and, based on time histories, calculate rates of deflection and viscous criterion (VC). The current study documents that these transducers are subject to damage affecting the linearity of their responses, that this damage is not uncommon, and that the deviations from linearity can greatly affect calculations of deflection rate and VC. A calibration procedure to identify transducers with significantly non-linear responses is proposed.

Foot-ankle injuries: influence of crash location, seating position and age

Foot-ankle injuries have increased in relative importance in recent years. As a basis for future countermeasures, an epidemiology study has been undertaken using Swedish accident data from Folksam Insurance. The database consists of 805 foot-ankle injuries out of 57,949 car occupant injuries reported from 1985 to 1991. The influence of crash location, seating position and occupant age is determined for the frequency, incidence and rate of foot-ankle injury in car crashes. Frontal car crashes produce 76% of the AIS 2-3 foot-ankle injuries with 13% in side impacts and 8% in roll-overs. The rate of AIS 2-3 foot-ankle injury is 24.7 per 1000 occupants injured in all crash locations and is similar irrespective of seating positions. Ankle fractures and sprains both occur at an incidence of 3.7 per 1000 injuries, followed by malleolus fractures at 2.7 and midtarsal fractures at 2.4. The foot-ankle injury incidence and rate are significantly greater (p < 0.01) in near oblique-frontal crashes than for 12 o'clock frontals. For drivers in 11 o'clock and front passengers in 12 o'clock, the incidence is 27.8 per 1000 injuries as compared to 17.5 for drivers and front passengers in 12 o'clock crashes. Occupant age is not as significant as seating position and crash location; however, there are higher incidences for rear occupants > or = 60 years old in oblique frontal crashes. Using the new AAAM Impairment Injury Scale (IIS), 48% of the foot-ankle injuries are rated with residual impairment IIS 1-2. The incidence in near-seated occupants is 1.5 times greater in oblique frontal crashes than in frontals. The incidence for IIS 1-2 impairment in near oblique-frontal crashes is 12.8 per 1000 occupant injuries as compared to 8.3 in frontal crashes.

Head impact tolerance: correlation between dummy impacts and actual head injuries

Forty-seven tests were run in which a baseball was pitched at an anthropometric dummy head at speeds of between 95 and 100 mph. Impact configurations included impacts to the front and side of the head with direct and indirect impacts. Tests were run with an unprotected dummy head and with the head protected with various helmets including baseball, football, hockey, bicycle, and motorcycle helmets. Head accelerations were measured for each test and maximum accelerations and Head Injury Criterion (HIC) values computed. The values of maximum acceleration and HIC for the tests to the unprotected dummy head were then correlated with actual injuries received by professional baseball players (without helmets) hit by fast pitches. Head accelerations and HIC values for helmeted tests are also compared to the results for the unprotected head to determine the relative effectiveness of each helmet design in attenuating impact.

A biomechanical analysis of head impact injuries to children

Head-first free falls of 30 children, 1-10 yr old, and one adult, 21 yr old, were studied 10 determine fall circumstances and injuries sustained. The falls of six children and one adult were simulated using the MVMA Two-Dimensional Crash Victim Simulator computer model. The data show that head-first falls of children onto rigid surfaces from heights as low as 2 m can result in serious injuries. Conservative head injury tolerance limits are estimated 10 be 200-250g for peak head acceleration.

The study has combined techniques of detailed investigation of selected human free-fall impacts and computer simulation of representative falls in order to expand knowledge of human impact tolerance. Of 2100 falls occurring in the U.S. and Canada, 110 cases were selected for on-site investigation of biomedical and biophysical factors. Seven head-first, two side-first, and three feet-first falls were then simulated using the MVMA 2-D Crash Victim Simulator. Children were generally injured less severely than adults under similar fall circumstances, and tended to land on their heads a greater proportion of the time. It was found that survival limits for children may be higher than previously believed. Body position at impact was a major factor in resulting injuries. In falls to rigid surfaces certain types of injury can be predicted on the basis of age and fall distance. For children under age 8 it is concluded that a constant acceleration of up to 350 G for 2.5-3 msec approaches the survival limit for head impacts. For children younger than 18 months the minimum limit tolerance level for reversible head injury may be reached when fall distance is somewhat greater than four feet.

Acute spinal-cord lesions from diving -- epidemiological and clinical features

Kewalramani, L.S.; Kraus, Jess F.Western Journal of Medicine
May 1977

Abstract

The aquatic activity that produces the greatest number of spinal-cord lesions is diving. Persons in the general population at greatest risk are males aged 15 to 19 years. Of the cases identified, 45 percent resulted from diving into a river or stream, 27 percent into swimming pools and 28 percent into lakes, reservoirs or the ocean. Distribution by age differed for the major groups of bodies of water. The incidence of spinal-cord injuries was related to season (spring-summer) and day of the week (weekends). The incidence of injuries was highest in those county areas with the least opportunity for exposure to swimming pools or rivers. Of the injured persons, 60 percent were tetraplegic at hospital admission. The most frequent radiologic finding was wedge fracture. This finding, in the absence of objective evidence that most divers struck the bottom of the water reservoir or a hard object, suggests that hyperventroflexion was the mechanism responsible for injury in most of the cases. Physicians and others should be aware of strategy options for preventing or reducing such injuries.

Study of human impact tolerance using investigations and simulations of free-falls

A study of free-fall accidents and resulting injuries was conducted to determine how useful these types of data could be in establishing human injury tolerance limits. “Tolerance” was examined primarily for children at two levels - reversible injury and threat to survival. The specific objectives were to investigate specific free-falls in sufficient depth to permit biomedical or mathematical reconstruction of the fall, simulate selected free-falls to estimate impact response, and compare predicted responses with observed injuries as a means of estimating human tolerance levels. From more than 2100 reported free-falls, 110 were investigated on-site. Seven head-first and three feet-first falls were then simulated using the MVMA 2-D Crash Victim Simulator. Newspaper reports of free-falls showed that males fell six times as often as females and most often while at work. Children fell from windows and balconies more often than from any other hazard. Case investigations showed that children were generally injured less severely than adults under similar fall circumstances, and tended to land on their heads a greater proportion of the time. The investigations also indicated that for impacts onto rigid surfaces: Both children and adults may be expected to suffer skull fractures in head-first falls of greater than 10 ft; adults are likely to incur lumbar spine fracture if they land in a sitting position after falling 10 ft; and adults will probably sustain pelvic fracture in feet-first falls of more than 30 ft. The head-first fall simulations predicted skull acceleration responses that were higher than previously considered survivable, although five of the six child subjects whose falls were simulated did survive. Analysis of simulation results indicated that, for some children under eight years old, peak accelerations of as high as 350 G, with a rate of onset of up to 200 000 G/s and a duration of up to 3 ms (approximate HIC = 1700-2800), would produce only moderate, reversible injury (as defined by AIS 2). For this same age group, the survival limit for head impacts - the level at which most people would sustain AIS 5 or greater injuries - was estimated to be as high as 600 G peak acceleration and 300 000 G/s for a duration of up to 3 ms (approximate HIC = up to 11 000). In feet-first simulations, the model predicted forces in the leg bones that correlated with observed injuries. The combination of in-depth on-site investigation and computer simulation of representative cases was found to be an effective method of studying impact injury tolerance.

Mid-sagittal dimensions of cervical vertebral bodies

A series of lateral radiographs of the cervical spinal column was evaluated in order to determine vertebral body dimensions. The sample included males (N = 30) and females (N = 31) 18 to 24 years old, comprising three stature percentile ranges (1–20; 40–60; 80–99) of the U. S. adult population. A two-dimensional analysis of vertebral body height (average distance between superior-inferior surfaces), depth (average distance between anterior-posterior surfaces), and area (average height × average depth) revealed minimal effects due to stature. In all subjects, average depth exceeded average height for vertebral bodies C3 through C7. Upon combining stature groups, both sexes revealed maximum average values for these dimensions at the seventh cervical vertebral body. Minimum average height occurred at C5 whereas minimum average depth was found at C3. Significant correlation ( < 0.05) was found for males between ponderal index and height and depth of the C7 vertebra. Male head weight correlated significantly with C3, C4, C5 and C6 vertebral body height and with C3, C5 and C6 vertebral body depth. For females, C7 height and C6 depth correlated significantly with ponderal index and head weight respectively. Probable biomechanical relationships of specific cervical vertebral bodies are noted.

Properties of the human neck which may influence a person’s susceptibility to “whiplash” injury during lateral impact have been studied in 96 normal subjects. Subjects were chosen on the basis of age, sex, and stature, and data were grouped into 6 primary categories based on sex (F,M) and age (18-24, 35-44, 62-74). Stature served as a secondary variable, with each group of 16 subjects being matched to obtain an average stature close to the 50th percentile for the category. The data include: measures of head, neck and body anthropometry in standing and normal seated positions; stretch reflex time of sternomastoid muscles; head/neck response to low-level acceleration; voluntary isometric muscle force in the lateral direction; and three-dimensional range of motion of the head and neck. Data are presented in a format applicable for biomechanical modeling of the seated human occupant and have been used in the MVMA-2D model adjusted for side impact at 10 and 30 mph to determine the influence of the measured properties on reducing “whiplash” injury susceptibility.

Biomechanical properties of the human neck in lateral flexion

Properties of the human neck which may influence a person's susceptibility to “whiplash” injury during lateral impact have been studied in 96 normal subjects. Subjects were chosen on the basis of age, sex, and stature and data were grouped into six primary categories based on sex (F, M) and age (18-24, 35-44, 62-74). The data include: measures of head, neck and body anthropometry in standing and simulated automotive seating positions, three-dimensional range of motion of the head and neck, head/neck response to low-level acceleration, and both stretch reflex time and voluntary isometric muscle force in the lateral direction. Reflex times are found to vary from about 30 to 70 ms with young and middle aged persons having faster times than older persons, and females having faster times than males. Muscle strength decreases with age and males are, on the average, stronger than females. Range of motion was determined by using three-dimensional photogrammetry to compute Euler angles relative to the Frankfort plane. Ranges of motion are reported for 6 planar movements (flexion, extension, left and right rotation, left and right lateral bend) and 3 combination movements (left rotation plus flexion, left rotation plus left lateral bend, and right rotation plus extension) chosen to simulate typical lateral impact conditions. For the young subjects, ranges of motion for males and females are similar. In all cases the range of motion decreases with age, with the rate of decrease for males being greater than that for females. Data are presented in a format applicable to biomechanical modeling of the seated human occupant.

A mathematical study of the effect of neck physical parameters on injury susceptibility

Analytical man motion models have been used to study how basic physical measurements may relate to susceptibility to cervical hyperextension-hyperflexion injury in an automobile collision. The parameters considered in the computer study are head-neck mass and moments of inertia, anthropometry, neck muscle strength, and location, as well as strength of motion-limiting “stops.” In addition, related environmental parameters such as seat structural properties and crash acceleration pulse have been included. The data used with the computer program span the range of physical and sexual variation in function and structure of the neck in a representative U.S. population and have been obtained in an extensive experimental program. Results are presented which attempt to relate injury susceptibility to physical stature, age and sex.

Cervical range of motion and dynamic response and strength of cervical muscles

Basic physical characteristics of the neck have been defined which have application to the design of biomechanical models, anthropometric dummies, and occupant crash protection devices. The study was performed using a group of 180 volunteers chosen on the basis of sex, age (18-74 years), and stature. Measurements from each subject included anthropometry, cervical range-of-motion (observed with both x-rays and photographs), the dynamic response of the cervical flexor and extensor muscles to a controlled jerk, and the maximum voluntary strength of the cervical muscles. Data are presented in tabular and graphic form for total range-of-motion, cervical muscle reflex time, decelerations of the head, muscle activation time, and cervical muscle strength.

Automobile head restraints -- frequency of neck injury claims in relation to the presence of head restraints

The study sample consisted of 67,143 insurance claims; the manual search of the files associated with these claims led to the identification of 6,833 struck cars meeting the study criteria. For these claims the following items of data were recorded for each forward car: model year, manufacturer, sex of the driver, and whether any type of neck or back injury was claimed. It was determined that there was an 18 percent reduction in the frequency of claimed neck injuries to drivers (both sexes combined) in cars with head restraints as standard equipment when compared with the frequency for drivers in cars without head restraints as standard equipment. Similar results by sex of driver are also presented. An analysis by manufacturer revealed differences similar to the overall pattern, but the numbers of observations when divided into these various subgroups were generally too small to support firm conclusions. The results of a visual survey of drivers in 4,983 moving domestic passenger cars with adjustable head restraints in the Los Angeles and Washington, D.C. Metropolitan areas indicated that in the Los Angeles area, 74 percent of the male drivers and 57 percent of the female drivers had the head restraints improperly positioned while in the Washington, D.C. Area 93 percent of the males and 80 percent of the females had the restraints improperly positioned. The study is concluded with a discussion of previous research on whiplash injuries and head restraints.

Parameter study of biomechanical quantities in analytical neck models

Bowman, Bruce M.; Robbins, D.H.SAE Technical Paper Series 720957
1972

Abstract

A parameter study is performed involving several analytical vehicle occupant models in current use, with investigation of neck representations a primary goal. Side, oblique, and rear impact situations are investigated. Attention is given to the effects of varying head-neck mass and moments of inertia, anthropometry, muscle strength, and location, as well as well as strength, of motion-limiting “stops.” A model that replaces the conventional simple ball-joint neck with a two-joint, extensible neck is studied. This model also makes use of joint-stop ellipses to approximate the anatomical range for relatively free angular motion at a joint. Allowance is made for the effect of muscle contraction on occupant dynamics as a function of the degree of voluntary or involuntary tightening of the muscles, based upon experimental findings. A discrete parameter neck model that treats the cervical spine as a linkage of rigid vertebrae and massless, deformable discs is discussed briefly. It is determined that, besides being extensible and having at least two joints, three-dimensional neck representations should account for coupling between the forces resisting the three possible rotational motions-yaw, pitch, and roll-that can occur between the head and the torso.

Basic physical characteristics of the neck which may influence a person's susceptibility to whiplash injury during rear-end collisions have been defined using 180 human volunteer subjects chosen, on the basis of sex, age (18-74 years), and stature, to be representative of the U.S. adult population. Measurements from each subject included anthropometry, cervical range of motion from both x-rays and photographs, and the dynamic response and isometric strength of the neck flexor and extensor muscles. Summary data for key measurements are discussed in the text; complete summaries for each measure are in four appendices. The results were used to develop a method of predicting dynamic muscle force from isometric EMG data, and to examine injury susceptibility for various population groups using a biomechanical model. The data are presented in a format usable in the design of biomechanical models, anthropometric dummies, and occupant crash protection devices. Experimental and modeling results suggest that the neck muscles can influence neck dynamic response to varying degrees for different population groups. Aging and sexual differences in cervical mobility, reflex time, and muscle strength were all found to be important factors in injury susceptibility.